Many authors have studied the links between levels of anti-dsDNA antibodies and disease activity in patients with SLE. Interpretation of these studies must take into account the facts that there are a range of possible assays for anti-dsDNA and a number of indices available for assessing disease activity. A recent study compared levels of various autoantibodies with organ specific disease activity assessed during the British Isles Lupus Assessment Group (BILAG) index. Anti-dsDNA and anti-heparan sulphate levels were more likely to be raised in patients with renal than non-renal disease. Some anti-DNA antibodies are actually anti-nucleosome antibodies, which lose DNA reactivity when purified under dissociating conditions. Patients with SLE have significantly increased levels of nucleosomes in their sera compared with healthy controls. In patients with SLE, reduced clearance of nucleosomes released from apoptotic cells may induce the formation of anti-nucleosome antibodies.